Tuesday

This is the way the bubble ends: not with a pop, but with a hiss. Housing prices move much more slowly than stock prices. There are no Black Mondays, when prices fall 23 percent in a day. In fact, prices often keep rising for a while even after a housing boom goes bust. So the news that the U.S. housing bubble is over won't come in the form of plunging prices; it will come in the form of falling sales and rising inventory, as sellers try to get prices that buyers are no longer willing to pay. And the process may already have started. Of course, some people still deny that there's a housing bubble. Let me explain how we know that they're wrong. One piece of evidence is the sense of frenzy about real estate, which irresistibly brings to mind the stock frenzy of 1999. Even some of the players are the same. The authors of the 1999 best seller "Dow 36,000" are now among the most vocal proponents of the view that there is no housing bubble. Then there are the numbers. Many bubble deniers point to average prices for the country as a whole, which look worrisome but not totally crazy. When it comes to housing, however, the United States is really two countries, Flatland and the Zoned Zone. In Flatland, which occupies the middle of the country, it's easy to build houses. When the demand for houses rises, Flatland metropolitan areas, which don't really have traditional downtowns, just sprawl some more. As a result, housing prices are basically determined by the cost of construction. In Flatland, a housing bubble can't even get started. But in the Zoned Zone, which lies along the coasts, a combination of high population density and land-use restrictions - hence "zoned" - makes it hard to build new houses. So when people become willing to spend more on houses, say because of a fall in mortgage rates, some houses get built, but the prices of existing houses also go up. And if people think that prices will continue to rise, they become willing to spend even more, driving prices still higher, and so on. In other words, the Zoned Zone is prone to housing bubbles.